In floor heat...without the heat?

Hey I think I have air in my radiant floor system...It is a closed boiler system. When it is running the supply lines get hot but after an hour or so the return lines are still cold...You can hear air in the system. I have a spirovent in it. I just really have no idea how to bleed it. Can someone tell me how? Is there anything I'm sposed to do with that spirovent? Like maybe open it or hit it or something? Please explain it like i'm a 5 year old-I know very little about this.

In floor heat...without the heat?

In floor heat...without the heat?

I don't see a purge set up on that piping. They may have purged it through the strainer when they originally installed it. An it can be done that way again. Shut off the valve at the boiler. Then shut off the one on the return at the manifold . Remove the strainer plug,(some water will come out). Then screw in a drain valve and connect a garden hose to it. Reopen the valve at the manifold, and the new drain valve, bleed/purge each loop separately, until no more air comes out. Close drain valve and valve at boiler. Leave the new drain valve in the strainer.

In floor heat...without the heat?

K...gotta get a couple parts to continue. When I drained it I'm sure glycol came out...got me thinking. If I flush it with water and the boiler decides to crap out, I may ruin the whole system if it freezes. With that said, it is normally just water in these systems correct?